1. Field of the Invention
The present disclosure relates to a fuse case and a case cover of a vacuum contactor in which a case cover is provided in a cradle side terminal part of a fuse case, preventing dielectric breakdown, and a protrusion type locking device structure is employed to facilitate attachment and detachment.
2. Background of the Invention
In general, a vacuum contactor is a high voltage electric device used for controlling opening and closing and protection to supply or stop AC power supplied to a motor, a transformer, a condenser bank, various switching systems, and the like.
In a power fuse combination vacuum contactor, among vacuum contactors, when a fault current is generated in a circuit, the fuse blows to break the circuit to protect a load device and the circuit.
FIG. 1 is a perspective view of a main body of a vacuum contactor according to a related art, and FIG. 2 is a perspective view of the main body and a cradle of the vacuum contactor according to a related art.
As illustrated in FIG. 1, a main body of the power fuse combination vacuum contactor includes a truck 1, a main circuit part 2 installed in an upper part of the truck 1, and a front cover 3 installed on a front side of the main circuit part 2. The main circuit part 2 has three phases, and each of the phases includes an upper terminal 4 and a lower terminal 5. A fuse is provided in each of the phases above the main circuit part 2. The fuse is connected to the upper terminal 4, and when a fault current is generated in a circuit, the fuse 6 blows to protect the circuit. The fuse 6 is installed in a fuse case 7. The fuse case 7 generally has a box shape with an open upper side to allow the fuse 6 to be installed therein.
Operations of the components are as follows. Power applied through the upper terminal 4 to which a power source side terminal is connected is transferred to a load side terminal connected to the lower terminal 5 through the fuse 6 and a vacuum interrupter (VI) (not shown) (which is installed within the main circuit part). When an abnormal current is generated during actuation of the circuit, the fuse 6 blows to break the circuit and the fuse case 7 prevents flash over of an abnormal transient voltage which has not been resolved. Thus, the fuse case 7 restrains flash over due to a high charge voltage of each of the phases (R phase and S phase and S phase and T phase) to prevent an inter-phase short accident, and prevents dielectric breakdown due to an introduction of a foreign object between phases.
FIG. 2 illustrates a state in which the main body of the vacuum contactor is inserted in a cradle 8. When the main body of the vacuum contactor is drawn in, the fuse case 7 is partially inserted into a terminal bushing 9 of the cradle. Thus, a side of the fuse 6 is completely insulated. Here, since an upper side of the fuse case 7 is open, if the fuse 6 is long, a front end portion is covered by the front cover 3 and a rear end portion is positioned within the terminal bushing 9, and thus, insulating performance is guaranteed. However, if the fuse 6 is short, a rear end portion (terminal part adjacent to the cradle) of the fuse 6 is exposed outwardly, leading to a possibility that dielectric breakdown occurs with a shutter 8a of the cradle 8.